1. Field of the Invention
The present invention relates to an FMCW radar locating device and a corresponding FMCW radar locating method.
2. Description of Related Art
Analyses have shown that a substantial number of traffic accidents are able to be avoided by the timely detection of dangers and by appropriately suitable driving maneuvers. The avoidance may be achieved by giving suitable warning signs to the driver or by automatic longitudinal and/or lateral control of the vehicle. One prerequisite for the awareness of the dangerous situation is suitable sensor devices.
Radar systems in the millimeter wave range have been used for some time now, as driver assistance systems for the awareness of danger. A distinction is made, in this context, between pulsed radar systems and continuous wave radar systems (CW). 77-GHZ-FMCW radar systems, for example, make possible the recording of objects within a range of a few centimeters to more than 250 meters. The distance of the objects and the relative speed of the objects with respect to one's own vehicle are ascertained simultaneously, as well as, in the case of an appropriate number of antennas, their angle to one's own vehicle's longitudinal axis, in this context.
In the usual FMCW radar systems, a signal is emitted which constantly changes in frequency. In order to limit the frequency range and to simplify the evaluation, several linearly rising or falling ramps are typically used.
FIG. 4 shows a representation of the time dependence (time t) of the transmitting frequency of a known FMCW radar locating device.
In FIG. 4, reference symbol FS denotes a transmitting signal and FE a corresponding echo signal. The quantity of the rate of change (slope steepness) of transmitting signal FS is constant in such known radar systems. If an echo signal FE is received, this has a transit time displacement, and thus has a frequency deviating from that of the transmitting signal. The distance from the measuring object, for instance, is able to be ascertained with the aid of frequency difference df.
Published German patent document DE 10 2004 034 429 A1 describes a radar locating system having a plurality of transmitting elements, at least two receiving elements and a device for the digital control of the processing of the receiving signals of the receiving elements, which operates according to the FMCW principle.